1. Field of the Invention
The invention relates to a fluid power transmitting device provided in a vehicle.
2. Description of Related Art
A vehicular fluid power transmitting device provided in a power transmission path between a power source of a vehicle and an automatic transmission is known. This vehicular fluid power transmitting device transmits torque generated by the power source to an input shaft of the automatic transmission via fluid. Some known examples of a vehicular fluid power transmitting device are a fluid coupling and a torque converter. A fluid coupling is provided with a pump impeller that is rotatably driven about an axis by a drive source such as an engine, and a turbine runner that is rotated about this axis by operating fluid that is pushed out by the pump impeller. A torque converter is described in Japanese Utility Model Application Publication No. 05-050202 (JP 05-050202 U) and Japanese Patent Application Publication No. 2010-84852 (JP 2010-84852 A). The torque converter is provided with not only the pump impeller and the turbine runner, but also a stator that is arranged between the pump impeller and the turbine runner, in a manner rotatable about the axis.
In such a vehicular fluid power transmitting device as that described above, a pump shell constitutes an outer shell of the pump impeller. Also, a center piece is provided with a center portion of the pump shell, that the center piece protruding toward the engine side. This center piece is fitted into a centering hole that is open in a shaft end surface of a crankshaft, such that the fluid power transmitting device is centered.
In JP 05-050202 U and JP 2010-84852 A, a damper device is provided between the pump shell and a drive plate that is fixed to a shaft end of the crankshaft. The center piece protrudes out from the pump shell. Also, the centering hole is open in the shaft end surface of the crankshaft such that the center piece is able to fit in the centering hole. In this case, relative rotation occurs between the center piece and the centering hole within a range within which relative rotation is allowed in the damper device such that the center piece and the centering hole slide each other. This sliding causes the center piece or the centering hole to wear, which reduces centering accuracy, and as a result, vibration of the vehicle may increase. One proposal as a countermeasure to this involves providing a bush or a bearing between the center piece and the centering hole, as described in JP 2010-84852 A. However, with the structure proposed in JP 2010-84852 A, there are also problems such as an increase in the number of parts; an increase in the number of processes, and an increase in the number of assembly hours.